Use destructuring assignments for named parameters (#180)

test/codegen/expect/unittest.js

 dart_library.library('unittest', null, /* Imports */[
   "dart/_runtime",
   'matcher/matcher',
   'dom/dom',
   'dart/core',
   'dart/async',
   'matcher/src/interfaces',
   'matcher/src/util',
   'matcher/src/description'
 ], /* Lazy imports */[
 ], function(exports, dart, matcher, dom, core, async, interfaces, util, description$) {
   'use strict';
   let dartx = dart.dartx;
   dart.export_(exports, matcher);
   function group(name, body) {
     return dart.dsend(dom.window, 'suite', name, body);
   }
   dart.fn(group, dart.void, [core.String, dart.functionType(dart.void, [])]);
-  function test(name, body, opts) {
-    let skip = opts && 'skip' in opts ? opts.skip : null;
+  function test(name, body, {skip = null} = {}) {
     if (skip != null) {
       core.print(`SKIP ${name}: ${skip}`);
       return;
     }
     dart.dsend(dom.window, 'test', name, dart.fn(done => {
       function _finishTest(f) {
         if (dart.is(f, async.Future)) {
           dart.dsend(f, 'then', _finishTest);
         } else {
           dart.dcall(done);
         }
       }
       dart.fn(_finishTest);
       _finishTest(body());
     }));
   }
   dart.fn(test, dart.void, [core.String, dart.functionType(dart.dynamic, [])], {skip: core.String});
   class TestFailure extends core.Object {
     TestFailure(message) {
       this.message = message;
     }
     toString() {
       return this.message;
     }
   }
   dart.setSignature(TestFailure, {
     constructors: () => ({TestFailure: [TestFailure, [core.String]]})
   });
   const ErrorFormatter = dart.typedef('ErrorFormatter', () => dart.functionType(core.String, [dart.dynamic, interfaces.Matcher, core.String, core.Map, core.bool]));
-  function expect(actual, matcher, opts) {
-    let reason = opts && 'reason' in opts ? opts.reason : null;
-    let verbose = opts && 'verbose' in opts ? opts.verbose : false;
-    let formatter = opts && 'formatter' in opts ? opts.formatter : null;
+  function expect(actual, matcher, {reason = null, verbose = false, formatter = null} = {}) {
     matcher = util.wrapMatcher(matcher);
     let matchState = dart.map();
     try {
       if (dart.notNull(dart.as(dart.dsend(matcher, 'matches', actual, matchState), core.bool)))
         return;
     } catch (e) {
       let trace = dart.stackTrace(e);
       if (reason == null) {
         reason = `${typeof e == 'string' ? e : dart.toString(e)} at ${trace}`;
       }
@@ skipping 23 matching lines @@
   }
   dart.fn(_defaultFailFormatter, core.String, [dart.dynamic, interfaces.Matcher, core.String, core.Map, core.bool]);
   // Exports:
   exports.group = group;
   exports.test = test;
   exports.TestFailure = TestFailure;
   exports.ErrorFormatter = ErrorFormatter;
   exports.expect = expect;
   exports.fail = fail;
 });